This invention relates to a foreceps device for use in an endoscope, and more particularly to a foreceps device having a pair of forceps levers intended to hold or resect a deseased organ portion within a body cavity, or to insert into the body cavity and operate a grip for gripping a deseased organ portion desired to be resected.
In this type of forceps device, the forceps levers thereof are inserted through the endoscope into the body cavity and are operated from outside of the body. As such forceps device there is known the one having such a construction as illustrated, for example, in FIG. 1.
A pair of forceps levers 1, 2 whose forward end portions are cup-shaped are commonly privotally supported, at their intermediate portion, on the forward end portion of a forceps holder 3. The base end portions of the pair of forceps levers 1, 2 are connected to a wire coupling through a pair of links 5, 4, respectively. To the wire coupling 6 is connected one end of an operating wire 7. As a result, a parallel link mechanism is constituted by the paired forceps lever 1, 2 and links 4, 5, and when the wire coupling 6 has been drawn or pulled rearwardly to permit the link mechanism to be rendered flat, the forward ends of the forceps levers 1, 2 perform the holding or gripping function.
In the forceps device having the foregoing construction, the relationship of the tractive force 2F of the wire coupling 6 with the gripping force 2W of the forceps levers 1, 2 is expressed by the equation: ##EQU1## WHERE R REPRESENTS THE DISTANCE BETWEEN A COMMON PIVOT FOR THE FORCEPS LEVERS 1, 2 AND ANOTHER COMMON PIVOT FOR ONE OF THE FORCEPS LEVERS 1, 2 AND A CORRESPONDING ONE OF THE LINKS 4, 5; M THE DISTANCE BETWEEN SAID COMMON PIVOT AND THE FORWARD END EDGE OF THE FORCEPS LEVERS; AND .theta. IS ONE HALF OF THE ANGLE DEFINED BETWEEN THE PAIRED LINKS 4 AND 5. In an actual forceps device, the relationship of l .apprxeq. r holds true. Accordingly, the above equation is rewritten as follows. EQU W .apprxeq. 2(r/m)sin .theta.
If it is assumed, therefore, that the tractive force be kept constant, the gripping force as applied by both forward ends of the forceps levers 1, 2 is maximum when .theta. = 90.degree., and becomes smaller as the .theta. is rendered small.
It is, however, necessary for an actual device that when the paired forceps levers 1, 2 are brought into a closed condition, namely, when the .theta. is made minimum, then the gripping force at the forward ends of the forceps levers 1, 2 should be made maximum. Accordingly, in such conventional forceps device, a pulling or drawing force exerted upon the operating wire 7 fails to become a gripping force of the forceps levers with high efficiency, so that the pulling force loss is large. As a result, where it is desired to permit the forceps levers to carry out a prescribed gripping operation, a considerably large tractive force is required. For this reason, the operating wire has to be so formed thick as to resist such large tractive force and simultaneously the related parts or sections have to be formed firm, which renders the forceps device itself bulky.